1. Field of the Invention
This invention relates to a liquid injection recording method and apparatus, and more particularly to a liquid injection recording method and apparatus which can effect stable droplet discharge even during continuous recording.
2. Description of the Prior Art
Non-impact recording methods have recently been attracting attention in that the noise occurring during recording is negligible.The so-called ink jet recording method (liquid injection recording method) which is capable of high-speed recording and of accomplishing recording without requiring any special process such as fixation on plain paper is a very effective recording method and various variants of it have heretofore been devised. Some of them have already been put into commercial use and some of them are being studied for practical implementation.
The liquid injection recording method is such that droplets of recording liquid called ink are caused to fly and adhere to a recording medium, thereby accomplishing recording, and such method is broadly classified into several types depending on the method of creating the droplets of recording liquid and the method of controlling the direction in which the created droplets fly.
The so-called drop-on-demand recording method, which causes droplets to be discharged and fly from discharge orifices (liquid discharge ports) in response to a recording signal and causing the droplets to adhere the surface of a recording, medium to thereby accomplish recording discharges only the droplets necessary for recording and therefore is nowadays particularly attracting attention due to the fact that any special means for collecting or treating the discharged liquid unnecessary for recording need not be provided. This in turn may lead to simplification and compactness of the apparatus itself, since the direction in which the droplets discharged from the discharge orifices fly need not be controlled and multi-color recording can be easily accomplished.
Also, in recent years, the development of recording heads (liquid injection recording heads) of the full line type with highly dense multiple orifices which uses the above-described drop-on-demand recording method has been remarkable and numerous liquid injection recording apparatus which can obtain images of high resolution and high quality at high speeds have also been developed.
In a liquid injection recording apparatus using the drop-on-demand recording method, pressure energy (mechanical energy) or heat energy is caused to act on the liquid present in the energy acting portion to thereby obtain the motive force for droplet discharge. Accordingly, it is necessary that such energy act on the liquid so as to be efficiently consumed for droplet discharge.
Also, where recording is to be executed continuously, it is necessary that the creation of such energy take place repetitively exactly in response to a recording signal. Particularly in the case of high-speed recording, it is necessary that such repetition be effected faithfully responsive to the recording signal imparted to the energy acting portion.
To enhance the quality of recorded images and enable high-speed recording to be accomplished, it is necessary to stabilize the direction of discharge of droplets, to prevent occurrence of satellites, to have droplet discharge executed stably, continuously and repetitively for a long time and to improve the droplet formation frequency (the number of droplets formed per unit time).
However, liquid injection recording apparatus using the drop-on-demand recording method has suffered from a problem that when the volume of droplets relative to the size of liquid discharge ports is very great, much liquid flies due to the discharge of droplets and therefore air is introduced from the droplet discharge ports when the retreat of the meniscus occurs. If air is introduced into the recording head, particularly into the energy acting portion for imparting discharge energy to the liquid or the vicinity thereof and thereby air is present as bubbles in the liquid in the recording head, the energy for discharging droplets will be consumed (absorbed) in compressing the bubbles. Accordingly, in some cases, the liquid may not be imparted the energy sufficient to enable the liquid to fly from the droplet discharge ports. That is, sometimes droplets cannot be discharged due to the bubbles. Also, even if droplets can be discharged, part of the discharge energy is absorbed by the bubbles and therefore it becomes difficult to cause droplets to land accurately on a recording medium. That is, in order that stable discharge of droplets may take place. it is important to prevent the introduction of air (that is, the presence of bubbles).
As the means for preventing the air from entering the energy acting portion or the like by reducing the retreat of the meniscus even if discharge of droplets is effected, there would occur to mind a method of pressurizing the liquid and overcoming the retreating force of the meniscus. However, where such method is used, it may occur that the liquid is forced out of the droplet discharge ports by the pressure of the liquid and the advantage of the drop-on-demand recording method which does not require a liquid collecting means is lost.
As a drop-on-demand recording method utilizing heat, there is a method wherein in causing droplets to be discharged from the discharge orifices, a heat-generating resistance member or the like which is a electro-heat converting member is used to impart heat energy to the liquid and thereby cause a change of state in which the liquid imparted the heat energy involves a steep increase in volume called gasification and the liquid is discharged by the acting force based on the change of state. In this case, the droplet discharge depends on the variation in volume of bubbles when the liquid is made into bubbles by the heat energy. The variation in volume of bubbles is determined by the area of the energy acting portion such as the heat-generating resistance member. However, to obtain a stable droplet discharge characteristic, an appropriate variation in volume of bubbles is necessary relative to the minimum cross-sectional area So of the discharge orifices, because if the variation in volume is too great, phenomena such as splash and introduction of air will occur to make the droplet discharge unstable or stop the discharge and if the variation in volume is too small, the circumference of the discharge orifices will become wet with the liquid to stop the discharge or make the discharge unstable. Also, if the variation in volume is small, no bubble will be created and accordingly, any variation in volume of bubbles will not occur and therefore no droplet will be discharged.